Apparatus for absorbing the secondary rays in x-ray photography



April 2, 1940. KAMM 2,195,729

APPARATUS FOR ABSQRBING THE SECONDARY RAYS IN X-RAY PHOTOGRAPHY Filed May 7, 1938 /nvenfor:

FM! WW Patented Apr. 2, 1940 UNITED STATES;

APPARATUS FOR ABSORBING THE SECOND- ARY RAYS IN X-RAY PHOTOGRAPHY Paul Kamm, Luzern, Switzerland Application May '7, 1938, Serial No. 206,552

In Germany January 19, 1937 2 Claims.

The invention relates to a secondary ray dia- I phragm for X-ray photography in which the lamellae forming the screen consist of juxtaposed vertical plates arranged side by side in groups,

5 the plates or lamellae of each group being of different heights and arranged so that their edges lie in planes approximately parallel to the marginal secondary X-rays. Secondary ray diaphragms were hitherto constructed chiefly so that the elements absorbing a large portion of the secondary and stray rays produced in X-ray photography, i. e., the lamellae, are placed approximately in the direction of the X-rays. This arrangement of the lamellae is necessary because thereby the shadow formation of the lamellae is redused as much as possible. The effect of the shadows which cannot be entirely prevented is rendered invisible by moving the screen in a suitable mannerduring the taking of the photo- 2 graph. This arrangement is, however, open to the objection that the source of the rays emitted by the X-ray tube must be very carefully centered to the diaphragm screen, this as is known presents particular 25 X-ray art. In the case of endless, band-shaped absorption screens moving for example like a conveyor band, such a construction and arrangement of the lamellae is almost impossible if it is not desired to use lamella controls the practical 30 construction of which is scarcely possible. Consequently in the German patent specification No. 578,443 it is proposed to make the absorption lamellae triangular in such a manner that the side walls standing on the base of the triangle extend parallel to the marginal rays of the X-ray field. By this shape a uniform impinging of the X-rays on the whole surface area of the diaphragm is taken into consideration but the triangular lamellae have a base width which impairs the whole construction of the diaphragm in the form which experience has shown to be advantageous. In the case of diaphragms with absorbtion elements of this shape the undesirable image of the individual lamellae on the X-ray picture could only be eliminated under certain conditions.

These objections are overcome by the invention without sacrificing the advantages obtained by the triangular lamellae according toGerman- 50 patent specification 578,443. This is attained according to the invention by constructing the lamellae or by fitting them together to form a screen in such a manner that the upper edges of the lamellae arranged in groups side by side 55 and of relatively diiierent heights so that the difiiculties in the medicinal upper edges of the lamellae of each group are in planes approximately parallel to the marginal secondary X-rays. If the upper edges of juxtaposed groups of lamellae are connected .by straight lines, these connecting lines form triangles whose sides are at an angle of about to the margin rays of the X-ray field.

As compared with the known apparatus for absorbing secondary rays in X-ray photography the invention presents several advantages. Thus, the individual lamellae, which as usual are made of a material which X-rays only penetrate with difficulty, for example lead, are first made as thin as paper whereby it becomes possible to make the distance between the lamellae as small as possible. However, experience has shown that l the smaller the spacing of the lamellae is," the greater willbe the absorption effect as regards stray and secondary rays. At the same time the shadow formation of the lamellae is itself reduced to a minimum. Furthermore, a centering of the X- ray tube is not necessary, as the. ray passage conditions in the case of a moved screen are uniform in the entire ray field in the range of practical perceptibility. For this reason the screens made according to the invention are particularly'suitable also for secondary ray diaphragms with endless screens and also for rotary disc diaphragms.

An embodiment of the invention is illustrated diagrammatically in the only figure of the accompanying drawing. v

l designates an X-ray tube which emits the beam of rays. 2 is a diaphragm whose screen is composed of several groups of lamellae ar- [ranged side by side. In the drawing for example three lamellae 3, 4 and 5 compose a group. In every two juxtaposed groups the individual lamellae are arranged in such a manner that the lines connecting the upper edges of the lamellae 3, 4 and 5 of neighbouring groups form the sides of an angle a which is approximately twice as large as the angle on formed by the X-ray beam and approximately equal to the angle formed by the marginal secondary X-rays.

The drawing clearly shows that in a screen thus constructed even the most unfavourably directed rays 6 of the X-ray beam have still to a great extent an unimpeded passage through the gap between the individual lamellae. 6 designates the photographic plate on which the primary rays emitted from the X-ray tube l act. I is the body to be X-rayed and whose image is to appear on the plate 6 and from which the stray and secondary rays 8 are radiated. From the 55 direction of these rays 8 it can be seen that they are caught by the lamellae of the diaphragm 2' 10 rays in X-ray photography, comprising vertical plate-shaped lamellae arranged side by side in groups, the lamellae of each group being of difierent heights and arranged so that the upper edges of the lamellae lie in planes approximately parallel to the marginal secondary X-rays.

2. A screen as specified in claim 1, in which the groups of lamellae are arranged side by side on a common base.

PAUL KAMIM. 

